Our long term objective is to relate the ultrasonic scattering properties of tissues to their structure and function, and to devise imaging systems that can show these tissue attributes to aid diagnosis. This project will make measurement designed to improve our understanding of the mechanisms whereby cardiac tissues scatter ultrasound. We will measure scattering cross-sections in absolute terms as a function of frequency, angle, and pathology. We will concentrate on tissues important for diagnosis of cardiovascular disease such as the heart and blood vessels. All phases of this work will proceed by using phantoms constructed of known physical materials to verity the accuracy of our methods and measurements on well characterized animal tissues, followed by investigations of human specimens. In-vitro studies of fresh dog tissues will be made in a computer controlled scanning tank which allows point by point measurements of amplitude and phase of scattered waves. From these data absolute scattering quantities can be derived using algorithms derived by ourselves and others. High resolution imaging of the scattering sites is important in determining the tissue components responsible for scattering. Such imaging methods will be explored using first, simulation, then the same data files generated in the measurement program. We will investigate, besides conventional imaging, large-aperature methods such as Fourier and Fresnel methods of wave equations inversion. This study will be extended to determine the effect of overlying tissues having different velocity of propagation and different attenuations, by incorporating these effects into the programs. We will attempt to implement methods of imaging that should be relatively immune the perturbing effects of overlying tissue. These make separate maps of compressibility that can, to a first order, be considered to be speed of sound.